Computers have become common place tools for professionals. They are invaluable for storing and processing large volumes of information and are often called upon to perform tasks involving calculations, statistics, graphics, computer-aided design, finances, business transactions, communications, etc. Indeed, computers have come to be ingrained in all facets of the workplace. However, as business needs dictate the travel requirements of today's professionals, there arose a need for a portable computer system. Hence, portable or "laptop" computers were developed to satisfy the demand for small, compact, and lightweight computer systems which could readily be carried and transported by an individual. These portable computers allowed professionals to bring their computers with them when traveling.
Although portable computer systems satisfied the demand for portability, their speed, power, storage capacity, and display functions were sacrificed in order to reduce its size and weight. Consequently, the portable computer was only used when portability became an issue. Otherwise, the standard desktop computer was the preferred computer system of choice. Hence, many professionals often have both a laptop computer as well as a traditional desktop computer. However, having two different computer systems had its own disadvantages. One serious problem related to file management. Since there exist two independent storage mediums--one per computer, there was a requirement to track the contents stored in each computer. A person would often wonder which computer had the latest copy. Another concern related to how the updating, copying, purging, and archiving of files were to be coordinated between the two computers.
A number of different solutions were attempted. One solution was to use a floppy disk to manually exchange and manage the files. This was a tedious, time-consuming, and generally error-prone method. An alternative solution was to use a software program to automate the copying and organizing process. This solution was often complicated due to the number of cables and software compatibility issues; it often created more problems than the portable computer solved. People found it was difficult to remember which computer had the latest information, or, whether files were current and contained their latest work.
To resolve these problems, a new solution was developed: the docking station. A docking computer is a portable computer/desktop computer solution whereby the portable computer retains its advantages of small size and weight, yet gains the full and robust features of a fully configured desktop system. Presently, the docking computer is in moderate use among professionals who frequently travel for business. It is estimated, however, that perhaps a majority of systems sold to mobile professionals will be portable computers with docking stations. The docking station is a device that enables a full-featured desktop environment at the office, while allowing the portability and convenience of a portable computer while traveling. The docking station essentially is the back plane and expansion slots of the desktop computer, while the CPU, DRAM and hard disk are part of the portable computing unit. This resolved the need for two computers as the computing and file information comes from only one computer--the portable computer.
Since the original docking station, there have been constant design challenges. The biggest challenge is to provide a docking system that is user-friendly and does not present information loss risk. The goal of docking computer devices is to allow the flexibility and portability of portable computers while providing the full featured robustness of desktop computers. In pursuit of this goal, three docking strategies have evolved: cold, warm and hot docking. Cold docking was the earliest of the docking systems. It consisted simply of turning off the portable computer and inserting it into or removing it from the docking station. This required the user to stop and restart/reinitialize (or reboot) the computer system each time the portable is inserted into the docking station, or removed from it. The user is required to have specific knowledge of the insert/remove and stop/reboot process.
Warm docking was developed to address some of the inherent limitations of the cold docking approach. In warm docking, the portable computer is set to a power managed state (in effect, neither on nor off) and inserted or removed from the docking station. Although the portable computer is not "off," it is operating in a reduced power state and is not functional to the user. In both cases, the system must be prepared by the user for the docking/undocking process in order to prevent data loss or damage to files stored on the system. Hot docking is the latest incarnation of the portable docking computer concept. Hot docking allows the insertion of a fully powered and operating portable computer into the docking station without concern about the state of the device's functional condition and the attendant worry of data loss or file corruption.
There are two ways to design a hot docking system in a PCI environment. The first involves the use of a PCI to PCI bridge on-board the computer device. The second method calls for a PCI to PCI bridge to be incorporated in the docking station. Referring to the first method, an on-board PCI to PCI bridge design incorporates the PCI to PCI bridge within the portable computer. With the on-board PCI to PCI bridge, the secondary PCI bus (i.e., the bus on the docking station) is isolated, and the portable computer system remains active (i.e., CPU and primary PCI cycles are allowed) during the docking process. The major disadvantage to this approach is that the PCI bridge and docking circuitry are located on-board the portable computer. This imposes a space, weight and cost penalty on the portable computer. In contrast, an off-board PCI to PCI bridge design moves the PCI to PCI bridge off of the portable computer and into the docking station. With the off-board PCI to PCI bridge, the primary PCI bus on the portable computer is extended through the docking connector and the PCI to PCI bridge provides the secondary bus within the docking station. With this design, the bridge chip and docking circuitry are located on the docking station, reducing weight, space and cost for the portable computer.
When designing either an on- or off- board bridge, not only must the PCI bus signals be isolated during docking and undocking, the ISA bus signals must also be properly isolated as well. Most portable computers today incorporate legacy ISA peripherals. In order to accommodate them, an ISA bus is provided on both the portable computer and the docking station. To join the ISA buses, the lRQ15:1! signals on both devices must be isolated during docking. This is being accomplished through the use of external glue logic, such as Quick-switches, or through the open-standard serialized IRQ/data protocol.
Although the use of Quick switches to electrically isolate the primary PCI bus from the docking station is undoubtedly more advanced than turning off the portable computer or switching the portable computer to a "power-managed" state, what is desired is a method to connect a portable computer system to a docking station without the added expense and complexity of incorporating Quick-switches. What is desired is a design which supports cold, warm, and hot docking methods, while minimizing weight, space and cost of component switches and chips on the portable unit. Additionally, the portable unit should be able to dock and undock from the station without requiring the use of a PCI to PCI bridge in the portable unit itself.
The present invention offers one such solution that accomplishes all of the above goals. These and other advantages of the present invention will become apparent within discussions of the present invention herein.